Biology Reference
In-Depth Information
these NPs offer biocompatibility, low toxicity, and easy modification of gold
structures to incorporate biofunctionality. For a review of the application
of AuNPs to a wide range of sensing applications, we recommend a 2012
article by Upadhyahula.
3
The synthesis of AuNPs was pioneered by Turkevich et al. in 1951, and
later refined by Frens et al. in 1973.
4
The typical method involves chemical
reduction of gold salts, e.g. of hydrogen tetrachloroaurate (HAuCl
4
) using
citrate, or sodium borohydrate,
5
as the reducing agent.
9.2.2. Silver nanoparticles
Like AuNPs, silver nanoparticles (AgNPs) have a typical size of 10-100nm
and can exhibit a wide variety of shapes. The advantages of AgNPs include
chemical stability, good conductivity, and excellent optical properties. AgNPs
have been employed for signal enhancement of AuNP detection schemes (see
Ref.
6
), although they have attracted most interest due to their optical prop-
erties because they are extraordinarily efficient at absorbing and scattering
light. Example applications include metal enhanced fluorescence and surface
enhanced Raman scattering. Additionally, like AuNPs, AgNPs display SPR,
which can be used for colorimetric detection and quantification of targets.
1
AgNPs are also well known for their antimicrobial properties. Silver
has been used for antimicrobial applications for thousands of years and,
recently, AgNPs have been incorporated into consumer products, primarily
due to these antibacterial and antifungal properties, such as clothes made
of AgNP-containing fabric
7
and personal hygiene products.
8
Others are
incorporated into wound dressings,
9
nano-silver toothpastes and colloidal
silver suspensions, designed as nutritional supplements.
10
There has also
been considerable interest in the use of nanotechnology in water purifica-
tion. In particular, the use of nanomaterials in small-scale, point-of-use, or
emergency response treatment systems has been proposed and investigated.
For example, silver embedded ceramic filters have been trialed in several
developing countries, and bactericidal AgNP paper was recently reported.
11
The synthesis of AgNPs is commonly performed via the reduction of
silver salts with reducing agents such as sodium borohydrate in the presence
of a colloidal stabilizer, including polyvinyl alcohol, bovine serum albumin,
or citrate. Green methods of synthesis have also been recently developed.
12
9.2.3. Quantum dots
Fluorescent quantum dots (QDs) are colloidal semiconductors with unique
optical properties when compared to conventional semiconductors, organic
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